They can be very interesting, both in the now and historically. They often aren't, when the problems were blindingly obvious and any mistakes ones that have been made countless times already, but the same can be said of success stories: without novel specifics there are only so many ways to say “we stuck at it and eventually pushed through and/or got lucky”.

Failure stories frequently aren't posted by the authors, they don't think it is interesting enough but someone else did. Such stories are often written as a post-mortem for those originally invested (in terms of intellectual interest, being a user of [thing-or-service], or financial investment) or even just as a therapy exercise before moving on, and not pushed to a wider audience by the author.

> failure posts are way less interesting than the authors think they are.

It depends; you can learn a lot more from a failure than from a success. Every success has some element of good luck in it but that element is difficult to identify.

Every failure has a number of non-luck related reasons for failing, which are usually easily identified.